1. Field of the Invention
The present invention relates to a tape player the operating mode is changed over by a mode changeover cam driven by a motor and, more particularly, to a mode changeover mechanism for changing over the operating mode of a tape player, having a mode changeover cam capable of surely and stably operating for mode changeover operation. This application is related to copending U.S. patent application No. 428,229, filed on Oct. 26, 1989 and co-owned U.S. Pat. No. 4,922,357.
2. Description of the Prior Art
Recently, tape players of a so-called logic control system using a motor for mode changeover operation have generally been used.
FIG. 11 shows a mode changeover mechanism for such tape players, disclosed, for example, in Japanese Utility Model Provisional Publication (Kokai) No. 62-8444. This known mode changeover mechanism has a magnetic head 42 mounted on a base plate 41 capable of moving in directions A and B. The base plate 41 is moved in the direction A to bring the magnetic head 42 into contact with a magnetic tape, and the base plate 41 is moved in the direction B to separate the magnetic head 42 from the magnetic tape. The base plate 41 is biased in the direction B by a spring 43. A changeover cam 44 for driving the base plate 41 is formed integrally with a mode changeover gear 45 meshing with a driving gear 46 which, in turn, is driven by a motor. When the mode changeover gear 45 is driven by the driving gear 46, the changeover cam 44 pushes the base plate 41 at a lug 41a formed by bending a portion of the base plate 41 to move the base plate 41 in the direction A against the resilience of the spring 43. The mode changeover gear 45 is provided with recesses 45a and 45b. The mode changeover gear 45 and the driving gear 46 are disengaged while the recess 45a or 45b is opposite to the driving gear 46.
The changeover cam 44 of this known mode changeover mechanism for a tape player has a very smooth cam surface to transmit a driving force through the lug 41a to the base plate 41 so that the base plate 41 is moved smoothly. In the stop mode as shown in FIG. 11, the lug 41a is in contact with the lowest point 44a of the changeover cam 44, namely, a point corresponding to the bottom of the stroke, and the base plate 41 is at the limit position of movement in the direction B. In a play mode in which the magnetic head 42 is in contact with the magnetic tape, the lug 41a of the base plate 41 is in contact with the highest point 44b of the changeover cam 44, namely, a point corresponding to the top of the changeover cam 44, and the base plate 41 is at the limit position of movement in the direction A.
However, since the smooth cam surface of the changeover cam 44 has no portion for stably holding the base plate 41, it is impossible to hold the base plate 41 stably at a desired position and the changeover cam 44 is liable to run beyond a desired position. For example, in the play mode, in which the point 44b of the changeover cam 44 is in contact with the lug 41a, it is possible that the changeover cam 44 is turned by an external shock to allow the base plate 41 to move, because the point 44b of the changeover cam 44 is in an unstable line contact with the lug 41a. In changing the operating mode of the tape player from the play mode to the stop mode by turning the changeover cam 44, it is possible that the base plate 41 is not placed stably at the position for the stop mode as shown in FIG. 11 due to the inertial turning of the changeover cam 44 and the mode changeover gear 45 beyond a predetermined position after the lowest point 44a of the changeover cam 44 has come into contact with the lug 41a. When a switch SW, which is closed by the base plate 41 when the base plate 41 is moved to the position for the stop mode as shown in FIG. 11, is employed for detecting the operating mode of the tape player, the switch SW will be closed once upon the arrival of the base plate 41 at the position for the stop mode, and then the switch SW will be opened if the base plate 41 moves in the direction A due to the excessive turning of the changeover cam 44 beyond the predetermined position. Such an accidental operation of the switch SW causes erroneous mode detection.